Too long to quote:
http://marc.theaimsgroup.com/?t=105538879600001&r=1&w=2
Wouldn't you get most of the benefit from copying that stuff around in
the driver if you allocated the skb->data aligned in the first place?
There's already code to align them on CPU cache boundaries:
#define SKB_DATA_ALIGN(X) (((X) + (SMP_CACHE_BYTES - 1)) & \
~(SMP_CACHE_BYTES - 1))
So, do something like this:
#ifdef ARCH_ALIGN_SKB_BYTES
#define SKB_ALIGN_BYTES ARCH_ALIGN_SKB_BYTES
#else
#define SKB_ALIGN_BYTES SMP_CACHE_BYTES
#endif
#define SKB_DATA_ALIGN(X) (((X) + (ARCH_ALIGN_SKB - 1)) & \
~(SKB_ALIGN_BYTES - 1))
You could easily make this adaptive to no align on th arch size when the
request is bigger than that, just like in the e1000 patch you posted.
--
Dave Hansen
haveblue@xxxxxxxxxx